Neuromorphic electronics that mimic the working principles of neuron and synapse behavior may change the computing paradigm, providing cognitive data processing capabilities. Artificial neuromorphic systems are highly productive due to parallel computing and thus tolerant to defects in circuits, consume low energy due to short spike-like electric pulses, and have reduced circuit complexity due to two terminal structures. Analog adaptive electronics may outperform currently used digital computing platforms in tasks such as image recognition, classification, cognitive computation and sensor data processing.
The memristor, a basic component of neuromorphic systems, is an electrical resistance switch with the capability to retain a state of resistance based on the history of applied voltage and flowing current. Memristor devices can store and process information in contrast to conventional integrated circuit technology where switching transistors and memory are separated. There are several classes of memristors, for example two-terminal vertical-stack, two-terminal planar, or three-terminal resistance switches. Based on the switching mechanism the materials can be grouped into two main categories—chemical and physical switches. The first class includes ionic switching materials where anions or cations are considered to be the mobile species utilizing the principles of redox reactions and nanoionics. Anion motion induced by an electric field leads to valence changes of the metal causing the resistance change of the material (such as metal oxides, metal nitrides, metal iodides and metal chalcogenides), while cation-based devices are driven by electrochemically active metals such as copper or silver with the capability of forming an atomic bridge between electrodes. A second category of memristors based only on physical changes include devices relying on magnetic, ferroelectric, electron/hole trapping and phase-change processes. However, both chemical and physical switching mechanisms can also be realized in a single device.